The objective of this project is to determine the clinical significance of alterations of levels of prekallikrein (Fletcher Factor) in man. Procoagulant and antigenic assays for prekallikrein (Fletcher factor) will be done serially in patients with intravascular coagulation syndromes, inflammatory diseases (rheumatoid arthritis, disseminated lupus erythematosus, dermatomyositis), allergic diseases (urticaria, asthma), septic shock, burn patients, renal diseases, and newborn infants with the idiopathic respiratory distress syndrome (IRDS). Normal controls will include adults, children, term and preterm infants, pregnant women, and volunteers receiving aspirin and corticosteroids. Detailed in vivo studies of the fibrinolytic mechanism, leukocyte migration, cutaneous inflammation, and endotoxin challenge will be performed in the subjects with hereditary absence of prekallikrein.